China was today engulfed by pollution more than 20 times higher than world safety levels for the second time in two weeks.

The thick smog forced airlines to cancel flights and prompted government warnings for residents to stay indoors.

Outlines of buildings in capital Beijing receded into a white mist as pedestrians wore face masks to guard against the thick, caustic air.

The US Embassy reported a peak level of PM2.5 - one of the worst pollutants - at 526 micrograms per cubic metre, or “beyond index”, and more than 20 times higher than World Health Organisation safety levels over a 24-hour period.

Reuters

Protection: Residents are forced to wear face masks to guard against the air

Liu Peng, an employee at a financial institution in Beijing, said he would keep his newborn baby indoors.

He said: “It’s really bad for your health, obviously. I bike to work every day and always wear a mask.

“The pollution in recent years is probably due to the increase in private cars and government cars.”

Visibility was less than 100m in some areas of eastern China and the government said, because there was no wind, the smog would probably not dissipate quickly.

More than 100 flights were cancelled in the eastern city of Zhengzhou, 33 in Beijing, 20 in Qindao and 13 in Jinan.

And the smog has come at the worst time for the country.

Reuters

Danger: Pollution is 20 times higher than the WHO safety levels

Every year, China’s transport system bursts at the seams as tens of millions of people travel for the holiday surrounding Chinese New Year on February 10.

Ren Haiqiang, a bank worker in his early 30s, said: “Travelling over the holiday is already a huge hassle, along with all the gift-giving and family visits.

“We thought flying would be the best way to avoid the crush, but if the weather continues like this we’ll be in real trouble.”

Air pollution has long been a problem in Beijing, but the country has only been more open about releasing statistics for some of the worst kinds of pollutants since early last year.